The present invention relates to a method for producing a metal strip that can be coiled into a coil in a continuous horizontal strip casting installation, and a horizontal strip casting installation for carrying out this method.
A traditional continuous strip casting installation for producing a coiled metal strip includes first a furnace (holding furnace or hot top) with a chill mold, which determines the cross section of the metal strip. The chill mold typically is flange-mounted at the outlet of the furnace.
A draw-off unit with several draw-off rolls is arranged at a distance from the chill mold. The metal strip is guided horizontally through the draw-off unit between several draw-off rolls extending horizontally. Of the draw-off rolls, at least one draw-off roll is driven. As a rule, however, several draw-off rolls are driven.
If needed, a milling unit for machining the surface of the metal strip may be integrated between the chill mold and the draw-off unit.
The metal strip is guided further in a horizontal plane from the draw-off unit to a coiling unit. The coiling unit is provided with several coiling rolls, which bend the metal strip so that it is deposited in the form of a coil after leaving the coiling unit. The coil is stored on supporting rollers that extend horizontally and are provided above the coiling rolls in the coiling unit.
The coiling unit itself is mounted on rollers and is movable by the metal strip relative to a stationary machine stand.
Between the draw-off unit and the coiling unit there is a strip cutting unit, usually near the draw-off unit, which is movable in the longitudinal direction of the metal strip, is supported on rollers, and which cuts the metal strip when a coil has reached its predetermined diameter.
The drives for the draw-off rolls, the strip cutting unit and the coiling rolls are linked together by a programmable controller.
The coilable metal strip is produced in a Pilger-type reciprocating cycle having a forward stroke of approximately 15 mm and a return stroke of approximately 5 mm with a pause of approximately two seconds inserted between the individual strokes. The relative acceleration of the metal strip here amounts to approximately 4.5 cm/s.sup.2. During the entire production of the metal strip in a coil, the coiling unit is attached to the coil sitting on it, with the diameter of the coil increasing constantly, so the draw-off unit must overcome mass acceleration forces of up to approximately 25 tonnes (approximately 4 tonnes to 6 tonnes for the coiling unit, approximately 4 tonnes to 16 tonnes for the coil with its increasing diameter and approximately 2 tonnes for the strip cutting unit if the strip is to be cut). Furthermore, an inertial force of 250 kN must be accelerated and decelerated in each cycle, taking into account the strip draw-off force of approximately 2.5 tonnes.
The coiling unit is shifted by the metal strip between two positions starting from the draw-off unit. A limit switch causes the coiling drive to be turned on and the coiling unit to move back to the starting position along the metal strip. Once it reaches this starting position, another limit switch is operated, turning the coiling drive off again. The distance traveled by the coiling unit amounts to approximately 500 mm. In this procedure, the masses indicated above are accelerated and decelerated back and forth intermittently up to 30 times a minute. With an increase in diameter of the coil and consequently also an increase in weight, the opposing forces become progressively greater, thus causing considerable stresses on the bearings for the coiling rolls but also on the other bearings which must be serviced constantly for this reason and replaced frequently. In addition, the specified draw-off parameters are altered so that reproducibility of the cycles is impossible. An operation with a greater number of cycles per minute is impossible.